December 6, 2006 THE CURIOUS COOK

When Science Sniffs Around the Kitchen By HAROLD McGEE

LAST week I went to Stanford University to hear a lecture on the molecular biology of smell, and then drove home buzzing with thoughts about what it might mean for people who love to eat. The speaker, the Nobel laureate Linda Buck, never mentioned food. She gave an overview of the fastdeveloping understanding of smell, including the pioneering work for which she shared the Nobel in Physiology or Medicine in 2004. Along the way she explained how, given what is known about the way smells are represented in the brain, the combination of two aromatic substances could create a third smell sensation that would be unlike the smell of either of the partners. And she presented evidence that certain aromatic chemicals — amines, which are found in the bodies of all animals and also in a variety of foods — trigger a brain circuit of their own. They act as pheromones in other animals, and may do the same in humans. I came away filled with new ideas about the alchemy of cooking. Can one flavor plus one flavor equal three flavors? How much of the effect of combining ingredients happens on the stove, and how much in people’s heads? Are there examples of this kind of virtual ingredient creation in familiar dishes? Can a rational awareness of flavor chemistry and amine circuitry influence and heighten our actual sensory experience of food? If we know more about how we smell, can we smell more? Does more sensation mean more pleasure? It was 30 years ago in a university library that I first stumbled across the scientific approach to food in the pages of Cereal Chemistry, The Journal of Food Science and similar publications. As I browsed through a couple of issues I couldn’t help grinning at the incongruity of high scientific language and high-tech instrumentation being applied to utterly ordinary, everyday things. It was strangely exhilarating to see such intellectual firepower aimed at the kneading of bread dough or the grilling of a hamburger or the mitigation of the gassy effects of beans, to be confronted with startling scanning-electron-microscope close-ups of the bacteria in yogurt, the mold in blue cheese, the surface of cooked spaghetti. At first it all reminded me of Lemuel Gulliver visiting Laputa and Balnibarbi, of severely cockeyed scholars eating geometric foods and trying to extract sunbeams from cucumbers. But the Swiftian thought quickly faded: this was funny, yet fascinating and substantial at the same time, something I just had to run out and share with my friends. Not long afterward I had my first book contract and a new career. Now, after three decades and two books about the science of cooking, that initially strange literature is familiar territory to me — familiar and still full of surprises. My heart leaps when I collect my mail and spot the blue-sky cover of The Journal of Agricultural and Food Chemistry. The superb library collections

in food and wine at the University of California, Davis, are less than two hours from my home, and I always feel an edgy anticipation when I exit Interstate 80 to immerse myself for a day or two in The Journal of Texture Studies, Aquaculture Research, Flavour and Fragrance Journal, Annals of Microbiology, Chemical Senses and American Journal of Enology and Viticulture. I never know what I’m going to learn, or by what remarkable means it will have been figured out. I haven’t collected the data, but I’m confident that never before in history have so many people in so many corners of the world used so many powerful instruments to peer into food — and into people as they consume food. Samples from my last immersion: physicists at the University of Nottingham, England, probe the surface of caramel with an atomic-force microscope to understand the molecular nature of its stickiness. A laser-scanning microscope at the French National Institute for Agronomic Research reveals bacteria in ripening Emmenthal cheese lining tiny pockets of milk fat, just where they can generate the most flavor. At the University of Bristol in England, gene-chip analysis — the marriage of DNA chemistry and silicon electronics — shows that the same variety of wheat expresses its genes very differently depending on whether it’s grown in conventional or organic conditions. Then there’s magnetic resonance imaging, the modern workhorse for looking within living things: in Japan, M.R.I. studies show how dry beans absorb water; in Denmark and Norway, how water moves into and out of pork when it’s brined and cooked; and in Rome and London, what parts of the brain sommeliers use as they taste and identify wines. This occasional column, the Curious Cook, will be a window on that big and busy world, on the endless intricacies of foods and the ingenuity of the people who make them and study them. The column is meant to share the buzz, to pass along news of interesting scientific research on food, cooking and eating. Because some of the larger issues are well covered elsewhere — nutrition, the influence of diet on longterm health, food production and the environment, genetically modified organisms — I’ll pay more attention to studies of particular foods, the kinds of subjects that originally drew me away from teaching literature and into the mysteries of emulsions and glutens and Maillard reactions. To start off: news that an old kitchen worry has now been explained in full and converted from a worry into an opportunity. I hear every year from cooks who have been alarmed at seeing normally pale garlic turn bright green and even blue, sometimes when the cloves are pickled whole, sometimes when they’re chopped and cooked with other ingredients. I’d often been puzzled by little blue-green specks when I made garlic bread with loaves of sourdough, but I was really rattled the first time I puréed raw garlic, onion and ginger together in a blender to make chicken in yogurt from Madhur Jaffrey’s “Invitation to Indian Cooking.” When I fried the purée the entire mass turned turquoise blue. I asked a couple of Indian friends who happen to be plant biologists whether they knew what was going on. They said they had never seen the blue purée, because Indian cooks don’t grind onions and garlic together. They grind or chop them separately and usually fry the onions first. For them, blue was the color of an American shortcut. For me it’s been a reliable curiosity every time I cook Ms. Jaffrey’s happily efficient recipes for chicken and cauliflower and okra, one that goes away as the purée browns and I add turmeric and the rest of the ingredients.

purée browns and I add turmeric and the rest of the ingredients. As I learned from one of my regular food-chemistry reads, it’s not necessary to see these color changes as problems. The northern Chinese think of them as attractive and auspicious. They make an intentionally intensely green pickle by aging fresh garlic heads for several months, then peeling the cloves and immersing them in vinegar for a week. The resulting Laba garlic pickle is served with dumplings to celebrate the New Year. According to chemists at the China Agricultural University in Beijing, aging the garlic gives it a chance to accumulate large quantities of one of the chemicals that generate the color; fresh garlic doesn’t green much at all. And a strong green color develops in Laba garlic only with acetic acid, the main acid in vinegar (also found in sourdough), because it’s especially effective at breaching internal membranes and mixing the cell chemicals that react together to create the green pigment. The pigment itself turns out to be a close chemical relative of chlorophyll, which gives all green leaves their color. Two recent reports from the House Foods Corporation in Japan detail exactly how the garlic and garliconion pigments develop. Their creators are the same handful of sulfur compounds and enzymes that give the allium family its unique pungent flavors. Under the right conditions these chemicals react with each other and with common amino acids to make pyrroles, clusters of carbon-nitrogen rings. These rings can be linked together into multipyrrole molecules. The ring structures absorb particular wavelengths of light, and thus appear colored. The two-pyrrole molecule looks red, the three-pyrrole molecule looks blue and the four-pyrrole molecule looks green, as does its cousin tetrapyrrole, the chlorophyll molecule. Like chlorophyll, all the pyrrole pigments are perfectly safe to eat. A mixture of onion and garlic favors a blue hue. All the pigments result from a combination of enzyme activity and simple chemical reactions, so you get the most intense color by puréeing the garlic and onion to mix enzymes thoroughly with their targets, then holding the purée on low heat to speed the enzymes without denaturing them, and finally heating it to a simmer to speed the nonenzymatic reactions. The tint can be muted through higher heat and faster cooking times, a procedure favored by Ms. Jaffrey, who is as unnerved as anyone when the onions in her pan turn turquoise. “I can’t bear that greenish color,” she said. “So I quickly sauté the paste to give it a more acceptable pinkish-brown hue.” So scientists have solved the mystery of the blue alliums. Which leaves curious cooks with a new challenge: how to use that knowledge to create a dish that celebrates the blue rather than toning it down. A homage to Krishna? Copyright 2006 The New York Times Company Privacy Policy

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